In an optical fiber radio system, development of interface technology that mutually converts a millimeter wave signal and an optical signal is important. Particularly in an uplink, a received feeble millimeter wave signal is first electrically amplified and then a laser or modulator is operated and problems such as a complex configuration of each base station and increased installation costs and power consumption are caused, projecting bottlenecks for widespread use thereof. Thus, Japanese Patent Application Laid-Open No. 2001-53542 discloses an antenna apparatus that converts a radio wave signal into an optical signal before reception or converts an optical signal into a radio wave signal before transmission.
However, the antenna apparatus disclosed by Patent Document 1 includes several series antenna elements. That is, Patent Document 1 does not intend to be used for a large-scale system and thus, it is difficult to use the antenna apparatus in a wireless LAN for mobile units. More specifically, Patent Document 1 does not establish the configuration of a large-scale array, connection technology between an antenna and an optical converter array, and optical loss compensation technology of a multi-stage light modulator and includes several series antenna elements.    Patent Document 1: Japanese Patent Application Laid-Open No. 2001-53542